单项选择题

Helicopters are set to motion by means of______.

A．one rotating fan in the centre of the aircraft and others at each end
B．a rotating fan underneath for lifting
C．a rotating device on top
D．a combination of rotating devices in front and on top

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单项选择题According to the passage, people expect that______.

A．helicopters could eventually replace the airliners of today
B．their imaginations fired by the Russian engineer's invention would be realized in the future
C．their fantastic expectations about helicopters could be fulfilled by airliners of today
D．helicopters would someday be able to carry millions of people from place to place as airliners are now doing

单项选择题According to the analysis, compared with normal children today, children treated for mental illness 50 years ago______.

A．were less isolated physically
B．were probably less self-centered
C．probably suffered less from anxiety
D．were considered less individualistic